After working in a shop for a few years, and seeing lots of different brands and sizes come through I am extremely wary of most "generic" generators out there. The engine and generator set are equally important. Cant tell you how many times I've seen units with Honda engines with gen set problems. Honda, Subaru and Yamaha all use Sawafuji on their stuff. This is why they command a premium. The Sawafujis very rarely fail with normal or even super heavy usage. The voltage regulators and windings are most common failure on the "generics" with parts usually not available locally. If you purchase a cheap generator, go ahead and get a replacement voltage regulator for it...odds are you will replace it at some point. Don't get Hung up on wattage ratings either. It's all about amps.
The difference between a true Japanese generator, and a Chinese unit is that one is a purchase, one is an investment. With propper usage and maintenance I have no trouble saying a Honda, Subie or Yamaha will last for 20 years or more.